During assembly of electronic components to mounting members, it is oftentimes important that the components be able to be precisely mounted in a predetermined position to provide for repeatability in assembly thereof. For assembly, the base member can be printed or coated with a layer of solder material thereon for attaching the die of the electronic component thereto. Automated vision systems can be utilized to locate contact points for wire bonding leads to the components attached on the base member. Where the component is to be utilized in a circuit, consistent location of the component is important to allow leads to be connected in a quick and efficient manner without having to take into account variations in locations of the contact points on the electronic component. However, where there is misalignment in the mounting of the component on the base member, the above-mentioned vision systems may not be able to adequately compensate for variations in the location of the wire contacts on the component assembly due to the misalignment. In addition, where the mounting member is a larger heat spreader for heat dissipation purposes, any shifting of the component on the spreader can reduce the efficiency of the heat transfer from the component to the spreader, and thus the heat dissipated from the spreader. In one known method for attaching components in proper alignment on mounting members, the component is placed onto the solder coat on the mounting member, and is ultrasonically welded by rapid agitation generated at the interface between the component die and the solder layer.
On the other hand, a reflow process for attaching electronic component dies and mounting members would be preferable over the above-described ultrasonic welding process. With a reflow process, high volume production of attached components can occur in an efficient manner with the parts being continuously run through a reflow oven. However, the problem in placing the components on the solder coated mounting members and running them through a reflow oven is that absent a mechanical fixturing and aligning device, the components are not restrained in the desired position for attachment to the mounting members. Thus, once the solder is heated and reflows in the oven, the component will be floating on a liquid layer of material such that any external forces applied to the floating component can cause it to shift from the predetermined position. Accordingly, any exhaust drafts in the oven, vibrations of the conveyor, etc. can cause the component to move on the liquid solder layer from the predetermined position. As described earlier, such movement or shifting is undesirable for subsequent wire bonding of leads to the component and for heat transfer purposes. Thus, there is a need for an assembly which accurately aligns and attaches the components in a predetermined position on a base mounting member in a consistent and repeatable manner by reflowing of a solid solder material therebetween to facilitate efficient high volume production of these component assemblies.
In one particular application herein, the electronic component is a power transistor and the base member is a larger heat spreader with the attached transistor and heat spreader being utilized in an automotive ignition module. In this application, the transistor generates heat and is also exposed to a high temperature environment in that it is engine mounted. At certain high temperatures, the durability of the transistor can be adversely affected; accordingly, it is important to keep the transistors below such critical temperatures for maximizing their performance. In this regard, the heat spreader is larger than the transistor die for proper dissipation of heat generated during use of the transistor. The larger heat spreader is coated with solder for attaching the transistor die thereto, and, if the solder is reflowed, the previously described problem of having the transistor component float and shift on the heat spreader will occur. Keeping the solder coated member to the same size as the die is not done in this application as the heat spreader must be larger than the die to properly dissipate heat from the transistor. Accordingly, there is a need for a transistor component assembly for manufacture thereof which keeps the transistor component aligned on the larger heat spreader and also keeps the size of the heat spreader sufficiently large to ensure proper heat dissipation from the transistor during use.